Sprocket with variable gear tooth valley radius

Abstract

A sprocket having a gear tooth valley radius which varies around the sprocket perimeter provides additional gear torque multiplication to a rider, which is especially beneficial when climbing hills. In some embodiments, the sprocket is a bicycle chainring with reduced gear tooth valley radius over at least a portion of the chainring. In other embodiments, the sprocket is a bicycle rear wheel cassette cog with increased gear tooth valley radius over at least a portion of the cassette cog. Regions of both reduced and increased gear tooth valley radius may be present on a given sprocket. The sprocket valley floor surface may be rounded or may include N segments adjoined by N vertices. The segments of the valley floor surface may be curved or straight. The vertices of the valley floor surface may be curved or angled. Embodiments for bicycles and motorcycles are presented.

What is claimed is: 
     
       1. A sprocket configured to engage with a cooperating chain having a plurality of chain rollers, each of the chain rollers separated by a distance of a chain pitch, the sprocket comprising:
 a plurality of gear teeth, a count of all of the plurality of gear teeth being a gear tooth number; 
 a plurality of gear tooth valleys, each of the gear tooth valleys being disposed between two adjacent gear teeth of the plurality of gear teeth and configured to engage with one of the plurality of chain rollers; 
 each gear tooth valley having a valley floor at a point nearest an axis of rotation of the sprocket, and a gear tooth valley radius measured from the axis of rotation to the valley floor; 
 wherein the sprocket has a nominal valley radius proportional to a product of multiplying the chain pitch and the gear tooth number; and 
 wherein the plurality of gear tooth valleys includes:
 a first set of gear tooth valleys comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having a reduced gear tooth valley radius which is less than the nominal valley radius; 
 a second set of gear tooth valleys, different from the first set of gear tooth valleys, comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having an increased gear tooth valley radius which is greater than or equal to the nominal valley radius; 
 the first set of gear tooth valleys being circumferentially offset from the second set of gear tooth valleys; 
 at least three of the first set of gear tooth valleys are included and circumferentially offset from one another; 
 wherein the first set of gear tooth valleys and the second set of gear tooth valleys together define a pattern core, and the pattern core repeats circumferentially at least three times; and 
 wherein the gear tooth valley radii of the gear tooth valleys in the second set of gear tooth valleys are equal. 
 
 
     
     
       2. The sprocket of  claim 1 , wherein the gear tooth valley radii of the gear tooth valleys in the first set of gear tooth valleys are equal. 
     
     
       3. The sprocket of  claim 1 , wherein the first set of gear tooth valleys and the second set of gear tooth valleys are present in an equal number, the equal number being from five to fourteen, inclusive. 
     
     
       4. A bicycle having a sprocket assembly including the sprocket of  claim 1 . 
     
     
       5. A motorcycle having a sprocket assembly including the sprocket of  claim 1 . 
     
     
       6. A sprocket configured to engage with a cooperating chain having a plurality of chain rollers, each of the chain rollers separated by a distance of a chain pitch, the sprocket comprising:
 a plurality of gear teeth, a count of all of the plurality of gear teeth being a gear tooth number; 
 a plurality of gear tooth valleys, each of the gear tooth valleys being disposed between two adjacent gear teeth of the plurality of gear teeth and configured to engage with one of the plurality of chain rollers; 
 each gear tooth valley having a valley floor at a point nearest an axis of rotation of the sprocket, and a gear tooth valley radius measured from the axis of rotation to the valley floor; 
 wherein the sprocket has a nominal valley radius proportional to a product of multiplying the chain pitch and the gear tooth number; and 
 wherein the plurality of gear tooth valleys includes:
 a first set of gear tooth valleys comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having an increased gear tooth valley radius which is greater than the nominal valley radius; 
 a second set of gear tooth valleys, different from the first set of gear tooth valleys, comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having a reduced gear tooth valley radius which is less than or equal to the nominal valley radius; 
 the first set of gear tooth valleys being circumferentially offset from the second set of gear tooth valleys; 
 at least three of the first set of gear tooth valleys are included and circumferentially offset from one another; 
 wherein the first set of gear tooth valleys and second set of gear tooth valleys together define a pattern core, and the pattern core repeats circumferentially at least three times; and 
 wherein the gear tooth valley radii of each of the gear tooth valleys in the second set of gear tooth valleys are equal. 
 
 
     
     
       7. The sprocket of  claim 6 , wherein the gear tooth valley radii of each of the gear tooth valleys in the first set of gear tooth valleys are equal. 
     
     
       8. The sprocket of  claim 6 , wherein the first set of gear tooth valleys and the second set of gear tooth valleys are present in an equal number, the equal number being from five to fourteen, inclusive. 
     
     
       9. A motorcycle having a sprocket assembly including the sprocket of  claim 6 . 
     
     
       10. A bicycle having a sprocket assembly including the sprocket of  claim 6 . 
     
     
       11. A sprocket configured to engage with a cooperating chain having a plurality of chain rollers, each of the chain rollers separated by a distance of a chain pitch, the sprocket comprising:
 a plurality of gear teeth, a count of all of the plurality of gear teeth being a gear tooth number; 
 a plurality of gear tooth valleys, each of the gear tooth valleys being disposed between two adjacent gear teeth of the plurality of gear teeth and configured to engage with one of the plurality of chain rollers; 
 each gear tooth valley having a valley floor at a point nearest an axis of rotation of the sprocket, and a gear tooth valley radius measured from the axis of rotation to the valley floor; 
 wherein the sprocket has a nominal valley radius proportional to a product of multiplying the chain pitch and the gear tooth number; and 
 wherein the plurality of gear tooth valleys includes:
 a first set of gear tooth valleys comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having a reduced gear tooth valley radius which is less than the nominal valley radius; 
 a second set of gear tooth valleys, different from the first set of gear tooth valleys, comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having an increased gear tooth valley radius which is greater than or equal to the nominal valley radius; 
 the first set of gear tooth valleys being circumferentially offset from the second set of gear tooth valleys; 
 at least three of the first set of gear tooth valleys are included and circumferentially offset from one another; 
 wherein the first set of gear tooth valleys and the second set of gear tooth valleys together define a pattern core, and the pattern core repeats circumferentially at least three times; and 
 wherein the gear tooth valley radii of the gear tooth valleys in the first set of gear tooth valleys are not equal. 
 
 
     
     
       12. The sprocket of  claim 11 , wherein the first set of gear tooth valleys and the second set of gear tooth valleys are present in an equal number, the equal number being from five to fourteen, inclusive. 
     
     
       13. A bicycle having a sprocket assembly including the sprocket of  claim 11 . 
     
     
       14. A motorcycle having a sprocket assembly including the sprocket of  claim 11 . 
     
     
       15. The sprocket of  claim 11 , wherein the gear tooth valley radii of the gear tooth valleys in the first set second set of gear tooth valleys are not equal. 
     
     
       16. A sprocket configured to engage with a cooperating chain having a plurality of chain rollers, each of the chain rollers separated by a distance of a chain pitch, the sprocket comprising:
 a plurality of gear teeth, a count of all of the plurality of gear teeth being a gear tooth number; 
 a plurality of gear tooth valleys, each of the gear tooth valleys being disposed between two adjacent gear teeth of the plurality of gear teeth and configured to engage with one of the plurality of chain rollers; 
 each gear tooth valley having a valley floor at a point nearest an axis of rotation of the sprocket, and a gear tooth valley radius measured from the axis of rotation to the valley floor; 
 wherein the sprocket has a nominal valley radius proportional to a product of multiplying the chain pitch and the gear tooth number; and 
 wherein the plurality of gear tooth valleys includes:
 a first set of gear tooth valleys comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having an increased gear tooth valley radius which is greater than the nominal valley radius; 
 a second set of gear tooth valleys, different from the first set of gear tooth valleys, comprising a plurality of adjacent gear tooth valleys each having a gear tooth valley radius and including several adjacent gear tooth valleys having a reduced gear tooth valley radius which is less than or equal to the nominal valley radius; 
 the first set of gear tooth valleys being circumferentially offset from the second set of gear tooth valleys; 
 at least three of the first set of gear tooth valleys are included and circumferentially offset from one another; 
 wherein the first set of gear tooth valleys and second set of gear tooth valleys together define a pattern core, and the pattern core repeats circumferentially at least three times; and 
 wherein the gear tooth valley radii of the gear tooth valleys in the first set of gear tooth valleys are not equal. 
 
 
     
     
       17. The sprocket of  claim 16 , wherein the gear tooth valley radii of the gear tooth valleys in the second set of gear tooth valleys are not equal. 
     
     
       18. The sprocket of  claim 16 , wherein the first set of gear tooth valleys and the second set of gear tooth valleys are present in an equal number, the equal number being from five to fourteen, inclusive. 
     
     
       19. A motorcycle having a sprocket assembly including the sprocket of  claim 16 . 
     
     
       20. A bicycle having a sprocket assembly including the sprocket of  claim 16 .